1. Technical Field
This invention relates to a method and apparatus of a demand oxygen controller and respiratory monitor for measuring and monitoring gaseous fluid flow and particularly gas flow from persons (patients, aviators, babies, miners, or divers).
2. Background
In the prior art, the practice is to use a fluidic sensor which only monitors breathing direction; or the method therefor has been adapted for demand oxygen control only but has not been adapted to mass flow or apnea detection.
3. This Invention
In this invention of the demand oxygen controller and respiratory monitor for mass flow measurement, the actual mass and direction of the gas, compensated for density and temperature, passing a certain point is measured. In flow measurement that does not compensate for density and temperature, the mass of the gas is unknown. In a mass flow measurement, the amount of gas molecules being either inspired or expired is known accurately because of the automatic compensation for density and temperature by the mass flow sensor. Thus, if a patient's expired breath is a different temperature than the inspired gas being fed to the patient, the mass flow, both ways, is accurately measured by the mass flow sensor and indicated by a particular output voltage in each respective direction. The patient is dependent upon the number of molecules of gas being supplied and this is dependent upon the barometric pressure and temperature surrounding the patient. Since the mass flow sensor is capable of accurately measuring mass flow regardless of the gas temperature, the oxygen demand controller can accurately control the mass of oxygen suppled to a patient regardless of whether the gas is supplied from an oxygen supply tank at room temperature or from a heated oxygen supply. For example, a pilot at a high altitude requires a higher flow rate of oxygen for the same mass per unit time than a deep sea diver inhaling oxygen at the higher barometric pressure. This is because there are more molecules of gas passing through the mass flow sensor at the higher barometric pressure. Thus, the arterial oxygen tension (P.sub.a O.sub.2) present in the blood stream is dependent upon the mass, not the volume, of oxygen inhaled at a specific barometric pressure. As a result, the percentage of oxygen present at a particular volume of gas must change in accordance with the barometric pressure. For example, a pilot must have a higher percentage of oxygen per breath than a deep sea diver in order a maintain a given arterial oxygen tension in the blood stream.
This apparatus is considerably smaller and less complex than previous devices. It has additional features such as mass flow rate, respiratory rate, and cessation of breathing.
*U.S. Pat. No. 4,570,631 attempts to detect apneic events through the use of a fludic means. This device is physically large and cumbersome. Its main purpose is to supply a high pressure pulse of gas or an electric shock to the patient to dislodge an obstruction or otherwise open the upper airway passage. It does not measure mass flow nor control the flow of breathing oxygen to a patient.